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 Post subject:
PostPosted: Dec Fri 21, 2007 2:50 am 
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Hi Curt

No argument from me... Going be interesting to see what Norm cooks up for next years project...

One thing proved for sure, if I can make it work probably anyone can... Except for looking over David's(tdkask)shoulder, I've never touched a regen...

Tom


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 Post subject:
PostPosted: Dec Fri 21, 2007 2:55 am 
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:lol: :lol:
Curt

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PostPosted: Dec Mon 24, 2007 8:45 am 
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Location: Collison, IL USA
I got experience with the 12K5 in a Knight Kit 12-in-One experimenter kit. It used solder jumpers where the new one use spring clips. It had a 12V supply with a selenium rectifier, filter and the tube under a shield. The radio circuit was a regen, it used (talk about cutting costs) an AA5 oscillator coil with a fixed cap across it to lower it's range, then a 100-150 pF compression trimmer with a shaft soldered on to the adjusting screw, then going out to a knob, for the tuning cap. It did tune nice and slow, about 10 turns from one extreem to the other, so it was as good as a Velvet Vernier!. To cover most of the Broadcast Band, there were 2 jumpers that cut in more fixed mica caps. Both open got 1100-1550, one in got 750-1200, both in got 600-850. The low end was pretty deaf, with all that capacity switched in. The best fun was chasing daytimers and locals in the 1200-1500KC area. I discovered the technique of grabbing daytimers when they were a bit tardy in shutting down, or early starting up, thus cheating by being on in the dark and "getting out" better. It was really pretty selective, with a 50-60 foot antenna and ground, I coupled the antenna by sliding the lead in and out of the RF coil. I wish I still had it, but it was given to me, so I passed it along to another newbie when I had learned what I could from it. It had several alarm, photoelectric and other projects. The transmitter could be heard all of 10 feet from my antenna, with a nasty sounding carbon mic.
The tube manual lists the 12K5 as wanting a 480 ohm (impedance) load. 12-15 mW audio. I have considered making a stereo headphone amp for efficient earbuds, using a tapped universal transformer. That's affordable tube Hi-Fi if carefully designed and built. I believe the 12U7 twin triode would serve as the input amp. Just beware that the innocent looking 12K5 is drawing a bunch of heater current. It gets as HOT as a 6V6, or 50C5. Ah nostalgia. I'll have to dig one out and get to work.

John Smith

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 Post subject:
PostPosted: May Sat 10, 2008 2:05 pm 
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BUMP

I've kicked this back to the main page, as a member asked to see the picts... Links now repaired...

Tom


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 Post subject:
PostPosted: Apr Mon 18, 2011 7:37 pm 
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oops


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 Post subject:
PostPosted: Apr Tue 19, 2011 5:31 am 
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I get an error when clicking on the pic links.

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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: May Fri 06, 2011 4:09 am 
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35Z5 wrote:
True to Norms design, except for a couple minor components, it's built with totally junk box items... Chassis has built in coil form... Worked first time out the gate... :shock:

Must have some parts that are too new, can only receive Radio Disney @ 1650 and one other station very weakly... Guess I need to learn a bit more about building regens...

Tom

Edited to allow pict as link to save load time...

http://mysite.verizon.net/a35z5gta/12k5a.jpg

http://mysite.verizon.net/a35z5gta/12k5b.jpg

Note all links repaired 5/10/08

Such a very amazing link!
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 Post subject:
PostPosted: May Fri 06, 2011 5:01 am 
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OK go back to first page, links are fixed...


Tom


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 Post subject:
PostPosted: May Fri 06, 2011 2:53 pm 
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Tom, I appreciate your booting thus thread up to the top again. It's an unusually worthwhile thread that shouldn't be buried.
Many thanks!

:wink:

Larry

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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Jul Sun 24, 2011 3:29 am 
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Location: Cambridge MN USA
Glad this thread got bumped up as I'm getting close to done with mine and still had some questions. Is a wirewound pot OK for the regen control? That's all I've got in that resistance range.

Like the person who started this thread a few years ago, I'm also using a CD container, but unlike his, I'm using a tall one. Plus I'm attempting to keep from mounting anything on the clear plastic part except the speaker and want to mount the regen control and the power jack on [a] separate bracket[s]. What have folks here used that looks good for this purpose?

As for the speaker I'm finding is that the average 5" speaker is actually 5-1/8", or about 1/4" too big to mount inside the top of one of these. If anyone has something that would fit or know where I can find one, please let me know. Note that I want something that's at least 4" in diameter.

Thanks,

Scott Todd


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Jul Sun 24, 2011 4:58 am 
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I have a wire wound pot in mine and it works, can't say if a carbon would be better, didn't have anything but the WW myself...

Tom


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Sat 06, 2011 11:09 pm 
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Location: Kurri Kurri, N.S.W., Australia
It sounds like the 12K5 is a real gem. How do you guys think this would work with a second 12k5 resistance coupled to it as an AF stage? Any recommendations for values? I'm still learning, and getting just past the 'model building/paint by numbers' stage.
It would be a real hoot to go camping in the mountains far away from interference as I do and take it as a small portable with its OWN 12v battery, different coils, and a longwire.


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Sat 06, 2011 11:48 pm 
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Welcome High Tension!!!

Since the 12K5 can only produce approx 35mw@12v, I'm doubting adding one as a single stage amp would make a big improvement, no doubt would be a try and see...

Seems I remember seeing a amp with a pair used in push pull, that should get close to 100mw output......


Tom


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Sun 07, 2011 2:30 am 
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Location: Cave Springs, AR
I get small room volume with 12k5 at 30VDC with a amp I built for my MP3 player.

I modified this ckt for stereo use

http://www.sophtamps.ca/mambo/index.php?option=com_content&task=view&id=26&Itemid=38

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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Mon 08, 2011 2:58 pm 
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Location: Kurri Kurri, N.S.W., Australia
Thanks for the welcome and the ideas! I've always had a fascination for radio and the regen circuits apeal to my preference for minimalism.

30v or there about isn't too bad. It's easy enough to make up a bank of cheap 9v batteries. The Sylvania data sheet I have says the 12K5 is a power amp driver. Any dieas what it was originally designed to drive?

I'm currently working on a 6V6 hikers2 variant to fit in a very nice 1920's radio case (original parts are just too dear and I have a few 6V6's). Small room volume on 27v so far, but the simplicity of the circuit is going out the window as I'm looking at another stage of AF and possibly an RF section. :roll:

Thanks again,

Lindsey


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Tue 09, 2011 11:46 pm 
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The 12K5 was used to drive the audio output transistor in the first low voltage, tube type car radios(IE ones without a vibrator, step up power transformer, etc)... That was mostly for the 1957 US models, in '58 about all mfgr's dropped the tube driver and went to a transistor... AFAIK the 12K5 was never used in a application that directly drove a speaker...

Tom


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Fri 17, 2012 7:05 pm 
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Location: Toronto, Ontario, Canada
Hello everybody,

I am building this radio http://oldradiobuilder.com/12vdiagram.pdf.

I am curious what should be the impedance of the primary section of my transformer. I understand that a single 12K5 calls for impedance of 800 Ohm, but what about this circuit?

Thank you.


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Fri 17, 2012 9:18 pm 
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looks like that circuit is using an inexpensive 70 volt line transformer
from a PA system.

Pete

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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Sat 18, 2012 1:23 am 
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"Line transformer" doesn't really say anything about the impedance as it could be anything from 1250 to 40k, assuming by "common 4 watt, 70 volt line transformer" he's referring to the Bogen T725. But who knows? It doesn't look like the Bogen, and he didn't bother to mention which taps are being used, but if I had to guess I'd say 1250, or so.


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 Post subject: Re: Norms 12K5 Regen Complete
PostPosted: Aug Sat 18, 2012 3:03 am 
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Location: Cambridge MN USA
That looks like a radio I'd like to build if I had the time. Unfortunately I don't. As to the transformer impedance, given that he's using a pair of 12K5s in parallel, I'd recommend the highest wattage tap which also represents the lowest Z- usually 5W on most 70V types.

Scott Todd


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